Conventionally, a semiconductor power device is used in a power amplifier circuit, a power supply circuit, a motor drive circuit, or the like. Performances such as a high breakdown voltage, high-speed switching, and a low ON-resistance are required of the semiconductor power device. To meet these requirements, development of nitride semiconductor devices has been underway.
As the nitride semiconductor devices, gallium nitride (GaN)-based semiconductor devices using heterojunction of a HEMTs (High Electron Mobility Transistors) and HFETs (Heterojunction Field Effect Transistors) are proposed.
Conventionally, in order to form an n-GaN layer, n-impurity ions are implanted into a part of a p-GaN layer. However, in this case, the resistance of the n-GaN layer possibly rises because of the implantation of the n-impurity ions into a p-region. Furthermore, when the impurity concentration of the p-GaN layer is lowered so as to reduce the resistance of the n-GaN layer, the contact resistance between the p-GaN layer and an electrode located thereon is increased. For these reasons, it is difficult to realize the low ON-resistance of a vertical GaN-based semiconductor device.